Datasheet

DeviceAddress
0 1 0
0
A1
A2
A0
Slave Address
R/W
Fixed
Hardware
Selectable
ControlRegisterandCommandByte
0 0 0 0 B1 B00
0
PCA9554
www.ti.com ........................................................................................................................................................SCPS128B–JULY2006–REVISEDAUGUST2008
Figure4showstheaddressbyteforthePCA9554.
Figure4.PCA9554Address
AddressReference
INPUTS
I
2
CBUSSLAVEADDRESS
A2A1A0
LLL32(decimal),20(hexadecimal)
LLH33(decimal),21(hexadecimal)
LHL34(decimal),22(hexadecimal)
LHH35(decimal),23(hexadecimal)
HLL36(decimal),24(hexadecimal)
HLH37(decimal),25(hexadecimal)
HHL38(decimal),26(hexadecimal)
HHH39(decimal),27(hexadecimal)
Thelastbitoftheslaveaddressdefinestheoperation(readorwrite)tobeperformed.Whenitishigh(1),aread
isselected,whilealow(0)selectsawriteoperation.
Followingthesuccessfulacknowledgmentoftheaddressbyte,thebusmastersendsacommandbytethatis
storedinthecontrolregisterinthePCA9554.Twobitsofthiscommandbytestatetheoperation(readorwrite)
andtheinternalregister(input,output,polarityinversionorconfiguration)thatwillbeaffected.Thisregistercan
bewrittenorreadthroughtheI
2
Cbus.Thecommandbyteissentonlyduringawritetransmission.
Onceacommandbytehasbeensent,theregisterthatwasaddressedcontinuestobeaccessedbyreadsuntila
newcommandbytehasbeensent.
Figure5.ControlRegisterBits
CommandByte
CONTROLREGISTERBITS
COMMANDBYTEPOWER-UP
REGISTERPROTOCOL
(HEX)DEFAULT
B1B0
000x00InputPortRegisterReadbyteXXXXXXXX
010x01OutputPortRegisterRead/writebyte11111111
100x02PolarityInversionRegisterRead/writebyte00000000
110x03ConfigurationRegisterRead/writebyte11111111
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